Recently, as mobile and multi-media industries have been developed, a demand on a flash memory device has increase. The flash memory device can be extensively used in devices capable of storing and occasionally updating system BIOSs of a networking device (e.g., a router, a hub, etc.), a mobile phone, a personal digital assistant (PDA), etc. The flash memory device also can be utilized in a memory card, a digital camera, a sound/image storage device, a solid state memory (SSD), a portable computer, etc.
Flash memory devices can be NAND type or NOR type. The NAND type has a disadvantageous random access characteristic during a read operation, but is advantageous for the high degree of integration and also is capable of performing a write operation through F-N tunneling. Therefore, the NAND type has low power consumption and is mainly used for a high capacity memory. The NOR type has the less degree of integration compared to the NAND type, and makes use of channel hot electron (CHE) injection during a write operation. Therefore, the NOR type has high power consumption, but performs a fast read operation through better random access characteristics. Thus, the NOR type may be used in a code memory of a mobile device.
To overcome the above limitations of the NAND and NOR flash memory device, U.S. Pat. No. 6,072,722 discusses an AND type in another form of a flash memory device. In a typical AND memory device, since memory cells are connected in parallel between a local bit line LBL and a local source line LSL, a write operation is possible through F—N tunneling. Therefore, the typical AND memory device has low power consumption during a write operation and performs a fast read operation. However, since the typical AND flash memory device arranges the local bit line LBL and the local source line LSL in a plane, a high degree of integration may be difficult to achieve. Furthermore, the AND flash memory device needs to apply a high write prohibit voltage to all bit lines not in use to reduce the likelihood of disturbing memory cells that shares a word line during a write operation.